This invention relates to power converters, particularly to that type of converter having a separate inductor with each of a plurality of choppers that are paralleled to form a multiphase chopper, and more particularly, though not limited to, a switching regulator operating with unity power factor for charging batteries.
There has been significant effort to develop viable passenger electric vehicles as one means of displacing future petroleum demand. To date, research and development emphasis has centered on battery and propulsion system technologies; little attention has been given to the battery charger. Production (off-the-shelf) battery chargers have the following typical characteristics:
1. Considerable Weight--typically 25 kg per kW of output.
2. Low Efficiency--typically 70% over the charge cycle.
3. Low Power Factor--typically 80% at full power.
4. Crude Control--maximum line current drawn not accurately limited; charge algorithm not adaptive to needs of battery.
5. Moderate Cost--typically $200 per kW.
Relative to an ideal charger, these characteristics significantly degrade both the performance and economy of passenger vehicles employing onboard chargers. It would be desirable to have as an ideal battery charger, one with significant improvement in each of these characteristics. The present invention based on a pulse width modulated chopper comes very close to achieving the ideal characteristics, namely a light weight, high efficiency battery charger which would achieve a near unity power factor at a low cost, and with insensitivity to line transients. However, although providing such a battery charger was the motivation for the present invention, it should be understood that any regulator involving alternating current would benefit from the present invention to enable operation with very near unity power factor. In fact, all applications of choppers used in power conditioning would benefit from the invention, such as line operated dc power supplies and line powered controllers for dc motors.
While conventional multiphase (two or more phase) switching converters significantly lower input and output ripple, compared to single-phase switching converters, they improve neither inductor nor switching device utilization. Consequently, another feature of the invention is to improve inductor and device utilization, and to reduce inductor losses.